Insulating glass units of the type commonly used in the fabrication of windows and doors comprise two or more spaced, parallel glass panes. The panes have confronting surfaces that are separated from one another by a peripheral spacer. One or more of the confronting surfaces may be coated with metal oxides or other materials to improve thermal efficiency of the glass units. The spacers, which often are tubular lengths of metal, extend around the periphery of the glass panes and are sealed to confronting surfaces of the panes by means of relatively soft, adherent sealant ribbons.
From a structural standpoint, spacers must support pairs of glass panes with respect to one another against stresses resulting from positive or negative windload due to thunderstorms or major atmospheric disturbances and from temperature variations in the interpane space due to solar heat gains and weather effects. The organic sealant ribbons referred to above generally are the weakest structural elements of the spacers, and because of their resilient nature, they do not restrain glass panes from in-plane or bending movements. Spacers employing organic sealants thus provide "simply supported" boundary conditions for the individual panes. On the other hand, ceramic frit and other rigid spacers that have been suggested in the prior art provide a rigid support approaching "clamped" boundary conditions. The probability of failure of glass panes under clamped boundary conditions from windload-induced stresses typically is much higher than that resulting from simply supported boundary conditions, and multipane structures using clamped boundary conditions thus tend to require the use of thicker or tempered (and therefore more costly) glass panes.
Spacers, in addition to exhibiting sufficient strength to enable an insulating glass unit to withstand wind, pressure and temperature differentials, must additionally support the panes with respect to each other as the glass units are fabricated, loaded, transported and unloaded, and as they are handled while being fitted into suitable frame structures. The stresses to which spacers are subjected during transportation and fabrication steps can be substantially more severe than stresses resulting from wind loading, particularly with respect to compressive forces which tend to compress the respective glass panes toward one another and thus crush the spacers separating them.
Spacers also perform a sealing function; they seal the interpane space (the space between confronting pane surfaces) from the atmosphere. The interpane space commonly contains dry air or an inert gas of low thermal conductivity, such as argon, and it is important that the interpane space be kept substantially free of moisture (which may condense) and even minute quantities of other contaminants.
Spacers should be highly thermally insulative. The gas-filled interpane space offers excellent resistance to the flow of heat. The bulk of the heat flow adjacent the periphery of insulating glass units occurs through the spacer because it is much more conductive to heat than is the gas in the interpane space. As a result, during wintertime conditions, the temperature of the inner or roomside pane peripheral area (usually considered to be a 21/2 inch wide strip around the periphery of the pane), especially near the bottom of the units, may fall below the dew point of air adjacent the roomside pane, causing undesirable condensation.
The "sightline" (the distance from the edge of the glass pane to the inner edge of the spacer) should ideally be as small as possible to maximize the vision area, and sightline dimensions often are required to be less than 3/4 inches or even less than 1/2 inches.
Thus, ideal spacers should provide simply supported (not clamped) boundary conditions to allow the glass panes to bend. Yet, the spacers should exhibit excellent insulating qualities and resistance to gas transmission. Finally, ideal spacers themselves should not unduly limit the viewing area.
Tubular metal spacers of the type described above generally have been made from aluminum by extrusion or metal bending processes, the hollow, elongated tubular spacers having generally flat opposed side walls which are adhered to confronting glass panes near their edges by means of adherent sealant ribbons. Spacers commonly are positioned inwardly slightly from the outer edges of the glass panes to define a trough or groove about the periphery of the insulated glass units; this periphery commonly is sealed with a sealant of silicone rubber or the like. The wall of the spacer that faces the interpane space may have grooves or slots through its thickness and may contain granules of a desiccant such as silica gel. In order to withstand the crushing loads to which spacers are subject during transportation and fabricating procedures, as described above, the tubular spacers commonly are made of relatively thick aluminum, e.g., aluminum having a thickness of 0.012 inches or more. Thick-walled aluminum spacers, however, readily transmit heat from one pane to the other and thus generally have poor insulating qualities. Tubular metal spacers can be made of stronger and less heat conductive materials, such as stainless steel, but even then the spacers must have thicknesses on the order of 0.009 inches or more in order to exhibit sufficient compressive strength to withstand shipping and handling stresses. As used herein, "compressive strength" refers to the resistance of a spacer to the crushing loads that act normal to the planes of the glass panes and which tend to crush the spacers between panes.
To reduce the severity of the problems referred to above, various spacer designs have been investigated. There is yet a substantial and unfilled need for a cost effective spacer which provides reliable structural support between pairs of glass panes, a small sightline, and which yet is highly insulative so as to resist the flow of heat through the spacer from one pane to the other.